The claimed subject matter relates, in general, to radio frequency (RF) power transistors, and more particularly, to radio frequency (RF) power transistors operating at a frequency greater than 500 megahertz (MHz) and dissipating more than 5 watts (W) of power. However, it should be understood that certain aspects of the claimed subject matter have applicability at frequencies below 500 MHz and/or below 5 Watts. For example, such a transistor could find particular utility in power supply and/or power management circuitry as well. Therefore, the term “radio frequency (RF) power semiconductor device” or “radio frequency (RF) power transistor” as used in this specification should not be construed as limiting the claimed subject matter.
The number of wireless applications has grown significantly over the past decade. The cellular telephone market is among the most pervasive of wireless technologies. The use of wireless devices is no longer considered a luxury but has become a necessity in the modern world. Wireless is by no means limited to cellular applications. Local area networks, digital television, and other portable/non-portable electronic devices are all moving towards having wireless interconnect. Not only is the number of different types of wireless devices increasing but increasingly higher data content may be transmitted and/or received. Increasing the content being delivered involves more bandwidth to transmit the data at a rate that is usable for the customer. For example, most cellular telephones are currently operating with second generation (2 G) or 2.5 G wireless infrastructures. Second generation wireless (2G) is known for the conversion from analog to digital technology for voice applications. The 2 G and/or 2.5 G wireless infrastructures may have limited capability to send large amounts of data or information to a user.
Third generation cellular (3 G) is an upgrade in cellular transmission capabilities to meet the demands for the transmission of higher content. An example of the higher content includes video information and real time access to the Internet. One area of licensed spectrum that will be utilized for 3 G is at a frequency of 2.1 gigahertz (GHz), which will be deployed having a minimum of 144 kbps packet-data service. Furthermore, there are plans for an enhanced 3G that involves transmission in the 2.6-2.8 GHz range. Although 4 G infrastructure has not been defined, it is predicted that higher frequency operation will be involved to provide the bandwidth needed for high data rate transmission. In particular, it is expected that 4 G wireless transmissions will be at frequencies greater than 3 GHz.
There are similar changes occurring in areas other than cellular such as television transmission wherein the federal government mandates the conversion to digital television within the next decade. The simultaneous transmission of high definition television (HDTV) further increases the complexity of the RF transmission equipment. Another area that is rapidly expanding wireless activity is wireless broadband for access to the Internet. What all of these applications have in common is the use of RF power transistors in power amplifiers (PA) that provide a power output from 5 watts to kilowatt levels.
The move to high frequency and high power transmission places enormous demands on the RF power transistor. RF power transistors are typically used in output stages of transmitters, for example in cellular base transceiver stations (BTS). The operating frequency for a cellular BTS can be as low as 450 MHz and as high as 2.7 GHz at this time. The power output of a cellular BTS is typically 5 watts and above. Moreover, the wireless industry is moving to standards that require increased linearity and lower distortion at the higher frequency of operation. Wireless interface technologies such as wideband code division multiple access (WCDMA) and orthogonal frequency division multiplexing (OFDM) involve high linearity to maximize data throughput and/or prevent spurious signals from being transmitted outside the transmission band.
The RF power transistor is typically used in a grounded source configuration. The predominant device being used for this type of high power radio frequency application has severe device design constraints when attempting to further extend frequency, operating voltage, and lowering distortion. Furthermore, thermal issues of the RF power transistor are involved as electrical design in a RF power amplifier and are addressed for higher power and higher frequency operation.
Various aspects of this claimed subject matter may be used alone or in combination with one another. For example, the design of an RF power transistor for cellular applications may address both the die manufacture and/or the package design. On the other hand, one or more embodiments may be utilized alone if the application specifications are not so demanding. Furthermore, other features and characteristics of the claimed subject matter will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.